1. Field of the Invention
The present invention relates to a map update data delivery technology.
2. Description of Related Art
Navigation apparatuses that provide guidance for the driver by displaying the current vehicle position on a map and retrieving, through a search, route information indicating a route to a destination have become increasingly common in recent years. Such a navigation apparatus holds map data, provided in blocks corresponding to the areal size of unit display areas for map display at the navigation apparatus, which enable the navigation apparatus to display the current position, execute route search and provide route guidance.
The navigation apparatus may obtain the map data in a recording medium such as a DVD (Digital Versatile Disc) or a recording device such as an HDD (Hard Disk Drive), or may download the map data via a communication network as is increasingly the case. However, the actual road network constantly changes with the construction of new roads, the closure of old roads, and changes in POI (Point Of Interest) information (facility information). For this reason, the user is able to perform a difference update of necessary map element data alone by selecting a specific data block as an update target so as to reflect the latest road conditions in the map data after the initial map data acquisition.
However, when the map element data in the data block selected by the user alone are updated in the difference map update, the map data integrity may be compromised. For instance, if a road, the data for which have been modified, extends beyond the selected block and only the data in the selected block are updated, the road may be discontinuous between the selected block and a block that has not been selected. Japanese Laid Open Patent Publication No. 2008-89852 addresses this issue by disclosing a technology for maintaining data integrity by correlating map blocks adjacent to one another and updating the data in another block if an update of the data in one block compromises the map integrity.
In addition, Japanese Laid Open Patent Publication No. 2006-317643 discloses a technology for maintaining the data integrity for sets of data that are referenced with one another by updating another set of data in the referential relationship as well if an exclusive update of a set of data may compromise the data integrity, in order to ensure that the map data do not become inconsistent through a difference update. Namely, the publication discloses a technology for integrating a series of update operations for maintaining the data integrity as a single transaction.